The present invention relates to a piezoelectric element and a method of manufacturing the same.
In prior art, there are known piezoelectric elements or materials having various structures, which are utilized as electric acoustic transforming element such as ultrasonic probe, such as shown in FIG. 11, in which FIG. 11A represents a piezoelectric element utilized for a one-dimensional array-type ultrasonic probe, FIG. 11B represents a piezoelectric element utilized for a two-dimensional array-type ultrasonic probe and FIG. 11C represents a piezoelectric composite material.
With reference to FIG. 11, reference numeral 101, 102 and 103 denote piezoelectric ceramic, filler and substrate, respectively, and each of the structures has an arrangement in which a number of fine plate-shaped or column-shaped piezoelectric ceramics are arranged and a filler of such as resin fills gap portions between the piezoelectric ceramics mentioned above such as shown in FIG. 11C. Further, it is to be noted that the term xe2x80x9cpiezoelectric ceramicxe2x80x9d used herein will mean inclusively piezoelectric ceramic layer or column.
For the array-type ultrasonic probes utilizing the piezoelectric elements such as shown in FIGS. 11A and 11B, it is necessary to transmit or receive ultrasonic waves from or to the individual piezoelectric ceramic, respectively, the divided piezoelectric ceramics are connected to drive circuits, respectively, through lead wires, not shown. On the other hand, in the composite piezoelectric material shown in FIG. 11C, electrodes are formed to both upper and lower surfaces, though not shown.
As mentioned above, in the general piezoelectric elements each having a structure in which a number of fine piezoelectric ceramics are arranged, which is manufactured by, for example, methods or processes described hereunder.
(1) One-dimensional Array-type Piezoelectric Element Such as Shown in FIG. 11A
First, there is prepared a flat plate of piezoelectric ceramic having a thickness coincident with a service (working) frequency of an ultrasonic probe (usually, a thickness of about xc2xd of a using ultrasonic wavelength), and the thus prepared piezoelectric ceramic flat plate is joined onto a substrate 103 or like. Then, the piezoelectric ceramic flat plate is cut one-dimensionally along one direction as shown in FIG. 11A by using a dicing saw so as to provide a preliminarily designed width. According to these processes, the one-dimensional array-type piezoelectric element shown in FIG. 11A, in which a number of piezoelectric ceramics are arranged, is manufactured.
(2) Two-dimensional Array-type Piezoelectric Element Such as Shown in FIG. 11B
The one-directional array-type piezoelectric element shown in FIG. 1A is cut by using a cutting machine such as dicing saw in a direction perpendicular to the preliminarily cut direction with a predetermined design width. That is, the piezoelectric ceramics 101 are cut so as to provide two-dimensional structure shown in FIG. 11B including a number of piezoelectric ceramic columns.
As mentioned above, in the prior art, one- or two-dimensional array-type ultrasonic probe could be manufactured by utilizing the piezoelectric elements or structures such as shown in FIG. 11A or 11B.
Furthermore, it was possible to manufacture a composite piezoelectric material such as shown in FIG. 11C by filling a filler 2 in grooves or gaps formed by cutting the piezoelectric ceramic columns of FIG. 11B.
In the prior art method of manufacturing the piezoelectric elements to be utilized for the ultrasonic probe such as mentioned above, however, fine or minute machine working by using such as a dicing machine was performed to a brittle piezoelectric ceramic, and accordingly, the piezoelectric ceramic was easily damaged or cracked, thus deteriorating the piezoelectric characteristics, or in the case of the array-type piezoelectric elements, the piezoelectric characteristics are not made uniform to the respective piezoelectric elements, and in the case of forming the composite piezoelectric material, the piezoelectric characteristics are locally deteriorated or made not uniform, thus providing a problem.
Moreover, in the prior art, also in a case where, according to requirement of viewpoints of acoustic matters or energy conversion efficiency, it becomes necessary to prepare a piezoelectric element having a structure of extremely narrow dimension between the respective piezoelectric ceramics and/or having a high aspect ratio, it was difficult to manufacture the piezoelectric element satisfying such structure or requirement. Furthermore, it was also very difficult to form a piezoelectric element or structure having a complicated shape such as having a curved surface.
Still furthermore, it is also difficult to effect fine or complicated working to the piezoelectric ceramic, and hence, the working is not so easily done, so that high yielding was not obtainable, also providing a problem. Particularly, in the case of manufacturing the piezoelectric element or material having grooved structure such as shown in FIG. 11B or 11C, it is necessary for the piezoelectric ceramic to be subjected to a number of workings or processes, so that it requires much working time and a problem of abrasion of a working jig such as dicing saw was raised.
An object of the present invention is to substantially eliminate defects or drawbacks encountered in the prior art mentioned above and to provide a piezoelectric element composed of fine piezoelectric ceramics having uniform and high characteristic particularly such as piezoelectric element arranged with piezoelectric ceramics having high aspect ratio or piezoelectric element having a curved surface which was difficult to be manufactured by a conventional machine working.
Another object of the present invention is to provide a method of manufacturing a piezoelectric element of the characters mentioned above with high yielding.
These and other objects can be achieved according to the present invention by providing, in one aspect, a piezoelectric element characterized in that a composite is formed from a piezoelectric precursor prepared by mixing a powder containing piezoelectric material with a binder material and a gap forming material filling a gap formed to the piezoelectric precursor and the gap forming material is then removed from the composite.
In preferred embodiments of the piezoelectric element of this aspect, the gap formed by removing the gap forming material is filled up with a filler.
The composite has sectional areas continuous at least in one direction so as to provide a same pattern.
The composite is formed by the piezoelectric precursor and the gap forming material in shape of sheets or plates, which are laminated in a predetermined order.
The composite is formed as a composite roll.
The composite is formed by laminating a plurality of composite plate members, in a thickness direction thereof, in which the piezoelectric precursor and the gap forming material are arranged at least in one direction perpendicular to the thickness direction thereof.
The composite is formed by laminating a plurality of composite plate members, in a thickness direction thereof, in which the piezoelectric precursor and the gap forming material are arranged at least in one direction perpendicular to the thickness direction thereof and piezoelectric precursors in form of sheets in a predetermined order.
The composite is formed by laminating a plurality of composite plate members, in a thickness direction thereof, in which the piezoelectric precursor and the gap forming material are arranged at least in one direction perpendicular to the thickness direction thereof and gap forming materials in form of sheets in a predetermined order.
The composite is formed by coating, in an overlapped manner, the piezoelectric precursor and the gap forming material both having fluidity so as to provide a predetermined pattern.
The composite is formed by applying the piezoelectric precursor in a mold formed of the gap forming material.
The above objects can be also achieved, in another aspect, by providing a method of manufacturing a piezoelectric element comprising the steps of:
preparing a piezoelectric precursor prepared by mixing a powder containing piezoelectric material with a binder material and a gap forming material;
filling a gap formed to the piezoelectric precursor with the forming material so as to form a composite of the piezoelectric precursor and the gap forming material; and
removing the gap forming material from the composite.
Furthermore, there may be provided an ultrasonic probe formed from the piezoelectric element mentioned above though not mentioned in detail herein.
According to the present invention of the characters mentioned above, there is obtained a piezoelectric element composed of fine piezoelectric ceramics having uniform and high characteristic particularly having high aspect ratio or having a curved surface which was difficult to be manufactured by a conventional machine working.
Furthermore, there is obtained a piezoelectric element in which a number of fine piezoelectric ceramics are arranged or which has a complicated curved surface, which has been extremely hard to be manufactured by the conventional machine working, can be manufactured at once with high precision and high yielding with low manufacturing cost.
The nature and further characteristic features of the present invention may be made more clear from the following descriptions made with reference to the accompanying drawings.